System for controlling electric motors used for the propulsion of a transport trolley

ABSTRACT

A system is described for the controlled propulsion of a transporting device including at least two drive wheels propelled by electromotive units, in which system at least two drive wheels are each propelled by independent electric motors; each electric motor receives electric power through an independent power amplifier which amplifies electric signals produced by sensor devices; the sensor devices detect a mechanical force applied on a push and pull element, and convert the mechanical force into electric signals which indicate the degree and the direction of the mechanical force applied on the push and pull element, and the amplifier amplifies the signal in accordance with a factor which is a function of the weight that the trolley has to move and it feeds the electric motor so it can power the drive motor in accordance with a torque corresponding to the movement ordered through the sensor devices.

TECHNICAL FIELD OF THE INVENTION

The present invention lies within the technical field of devicespropelled by an electromotive force and particularly in the sector ofdrive systems for electric trolleys and self-propelled devices.

STATE OF THE ART PRIOR TO THE INVENTION

At present, devices powered by electric motor, such as trolleys,fork-lifts or platforms for transporting loads, merchandise, pallets,crates, etc., jacks and self-propelled instruments like for examplemobile X-ray units, find application in a plurality of industrial andcommercial sectors.

Such devices are usually propelled by one or more drive wheels operatedby electric motors, with the facility for the operator to select betweenfunctions of start/stop, forward/reverse movement and, in some cases,travelling speed. This type of device is handled by an operator standingon the floor who controls the direction and, where appropriate, thetravelling speed by control means corresponding to the functionsmentioned. The control means are usually situated on a lever or barwhich, in order to direct the device to the left or to the right, isusually coupled to a frame or platform, having said frame or platformone or more wheels which turn freely and are swivel-coupled to the frontor rear part of the body of the device, so that the displacing of thebar or lever to the right or to the left permits the device to be turnedto the right or to the left.

These conventional devices, although very useful, have a number ofdrawbacks.

In this sense, a first drawback of the conventional devices is that byhaving the operations of turning to the right or to the left done bymanually positioning the direction of the free wheels, the possibilityof performing turns in confined spaces proves complicated. Furthermore,with this type of device, it also proves relatively complicated to moveat an adequate speed and, consequently, for safe and precise handling,training in handling is necessary.

The European patent application EP 0 253 333 describes a control systemfor providing power to independently driven wheels of a power drivencart for transporting medical diagnostic equipment. A manuallyengageable handle is mounted to the cart in a position allowing a personto exert a manual force on the handle in a direction in which it isdesired for the cart to move. Force sensors are coupled to the handle tosense the manual force applied to it in a plane parallel to the plane onwhich the cart is to be moved. The force sensors provide signalsrepresentative of the magnitude and direction of the manual forceapplied to the handle in forward, reverse and turning directions.Electronic circuits are coupled to the force sensors for providingcontrol signals to motors driving the wheels of the cart forindependently controlling direction and velocity of movement of thecart.

The features known in combination from this European patent are placedin the preamble of independent claim 1.

OBJECT OF THE INVENTION

The object of the present invention is to overcome the drawbacksmentioned above by means of a system which permits the controlledoperation of a device propelled by electric motor, which is easy tohandle without any need for intensive training, which can turn inconfined spaces and which, in spite of being an active motorisedelement, behaves with a certain pasiveness which translates into asensation of heaviness for the operator which contributes to theoperator's handling of the device being intuitive, very precise, easyand quick.

DESCRIPTION OF THE INVENTION

In accordance with the invention, the aforementioned objects areachieved by means of a system for the controlled operation of a devicepropelled by an electric motor which comprises at least two drive wheelsfitted at opposite ends of an axle, propelled by electromotive means,and control means for governing the propulsion of the drive wheels, inwhich each drive wheel is propelled by an independent electric motor andin that each electric motor is provided with independent control means.In accordance with the invention, these control means for each electricmotor comprise an independent power amplifier which amplifies electricalsignals produced by sensor means, and feeds electric power to theelectric motor. The sensor means detect the mechanical force of pushingand pulling applied to a push and pull element by a user, and transformssaid mechanical force into electrical signals indicating the degree ofthe force (e.g. strong, very strong or weak) at the direction (forwardor backward) of the mechanical force applied in said push and pullelement. The amplifier amplifies the signals in accordance with anamplification factor in terms of the weight of the device, and feeds theelectric motor so that it powers the drive wheel in accordance with atorque corresponding to the movement ordered by the sensor means. Thesensor means which order each electric motor can be operated separatelyin such a manner that each drive wheel can be propelled selectively.

In a preferred embodiment of the invention, the system comes with twowheels each propelled by its own electric motor as well as with firstcontrol means for the first electric motor and second independentcontrol means for the second electric motor. In accordance with thisembodiment, the first control means comprises first sensor meansrequired by a first push and pull means, and the second control meanscomprises second sensor means required by a second push and pull means.Preferably, the first and the second push and pull element, areinterconnected through a connecting element coupled in such a mannerthat pulling or pushing the connecting element by the user can actselectively on the first or the second push element.

In a preferred embodiment of the invention, the connecting element is ahandle whose extremities act respectively on the respective push andpull elements, which in turn act on the respective sensors. With thisarrangement, it is achieved that, by pushing or pulling the handle, theoperator is able to manoeuvre in an especially easy and comfortablemanner. Thus, when the handle is situated at the rear of the device andthe operator wishes to start to move forwards, he has only to grasp thehandle with both hands, one on the left part of the handle and the otheron its right part, and push it with the same force by both hands. Inthis manner, the extremities of the handle shall apply the same pressureon the two sensors which shall transmit the electrical signalscorresponding to their respective control means so that both electricmotors operate at the same speed. When the operator wishes to turn tothe right, he pushes the handle more firmly in his left hand, so thatthe control means on the left side order the electric motor on the leftto rotate at a greater speed than that on the right and, consequently,the left drive wheel turns more quickly than the right one and, if it iswished to turn to the left he pushes more firmly in his right hand inwhich case the control means of the right side and, consequently, theright side electric motor and the right drive wheel work in a way as thedescribed above with respect to the manoeuvre of turning to the right.When the operator wishes to start to reverse, he pulls the handleinstead of pushing it, in the same way as the described before withrespect to moving forwards.

When the operator wishes to turn the device around, he pushes the handlewith the opposite hand to that of the turning direction andsimultaneously he pulls the handle with his other hand. In this case,the motor and, consequently, the drive wheel of the side on which theoperator pulls the handle rotates backwards whereas the drive wheel onthe side on which the operator pushes the handle rotates on the oppositedirection, thereby making it possible for the device to turn aroundcompletely.

Likewise, the operator can select the travelling speed by simply pushingor pulling the handle with variable strength.

In a preferred embodiment of the system of the invention each of thecontrol means also comprises first preamplifier means which amplifiesthe electrical signals produced by the sensor means as a function of thepushing or pulling force detected, which feeds preamplified signals tothe power amplifier which supplies the drive wheel. In this preferredembodiment, it is also especially beneficial that each of the controlmeans comprises also for each power amplifier, a feedback circuit whichcompares, by comparator means, the true value of electric power suppliedto the electric motor with the pre-established value of electric powernecessary to achieve movement of the of the drive wheel, and transformsthe difference detected—which arise for example when the drive wheel ison a ramp sloping upwards or downwards—between the true value and thepre-established value, into error signals by means of which the inputelectrical signals to the power amplifier are altered in order that thelatter supply the necessary power to the electric motor for it to rotateon a basis of the torque required to perform the movement ordered by thesensor means. In this manner it is achieved that the unevenness of thesurface over which the device is travelling is automatically offsetinsofar as its possible effect on the motion of the device is concerned,and the movement is therefore uniform. Appropriately, each feedbackcircuit comprises a second preamplifier means which amplifies the errorsignals.

In an especially preferred embodiment of the system of the invention,the latter is incorporated into a mobile X-ray unit. It is well knownthese units are very heavy (400-600 kg, usually) and have to be capableof being manoeuvred often in very confined spaces, by personnel notaccustomed to handling this type of apparatus frequently.

According to the invention, the amplification factor applied to thepower amplifier is calculated so that a relation is maintained betweenthe weight of the propelled device and the application of a reasonableforce on the push and pull elements by the user.

As sensors for detecting the pushing or pulling force applied by theoperator, use can be made of load cells (like for exampleextension-measuring gauges), pressure detectors, and also piezoelectric,optical, magnetic, capacitive and resistive sensors.

As power amplifiers use can be made of standard instrumentationamplifiers and preamplifiers for the input signals, such as thosemarketed by the company ANALOGUE DEVICE.

DESCRIPTION OF THE DRAWINGS

The invention is described hereunder on the basis of an embodiment shownin the drawings attached hereto which form an integral part of thisdescriptive specification, in which:

FIG. 1 shows a schematic block diagram which shows the basic electronicand electrical elements of the system of the invention in an embodimentapplied to a device propelled by two drive wheels;

FIG. 2 shows a schematic block diagram, corresponding to FIG. 1, of thebasics elements related with the control of the left side drive wheel;

FIG. 3 shows a schematic plan view of the most significant components ofthe system in the embodiment illustrated in FIG. 1;

FIG. 4 is a schematic view of the disposition the handle, the left sideforce sensor and the left side push and pull element, shown in FIG. 3;

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

As can be appreciated from FIG. 1, the system comprises a force sensor 1which detects the mechanical force of pushing, +FI, or pulling, −FI,applied by the operator, and transmits signals indicating the forcesdetected to the power amplifier 2. The amplifier 2 amplifies the signalby a factor KI and supplies the resulting electric power to the left,direct current motor 3, which powers the left drive wheel 4. A feedbackcircuit 5 which measures the motor current which is proportional to thetorque, detects any difference between the nominal value and the truevalue and generates, in the event of there being differences betweenthese values, an error signal which is applied to the amplifier 2 inaddition to the signal received from the force sensor 1. FIG. 1 alsoshows the layout of the elements for controlling and propelling theright wheel, comprising the right force sensor 6 which detects thepushing +FD, or pulling forces, −FD, applied by the operator, the rightamplifier 7, the right electric motor 8, the right drive wheel 9 and theright feedback circuit 10. For the propulsion of the left wheel anentirely similar layout of elements is provided.

It can be appreciated from FIG. 2 that the left side feedback circuit 5comprises a preamplifier 11 for the error signal and anotherpreamplifier 12 for the signal received from the force sensor 1. Thelayout shown in FIG. 2 for the left side is entirely similar to thelayout of elements on the right side (not shown in FIG. 2).

FIG. 3 shows the physical layout of:

-   -   the force sensors 1, 6 comprising extension-measuring gauges        (VISHAY) 1 a, 6 a,    -   the electric motors 3, 8,    -   the drive wheels 4, 9 in a mobile X-ray unit 13,    -   the push and pull elements 14, 15 comprising spring metal bands,        anchored in respective fasteners 16, 17 of the unit 13        framework, said push and pull elements being joined to each        other, at their outside extremities, by means of a handle 18.        It can also be appreciated that, in the embodiment shown in FIG.        3, the power supply is a set of rechargeable batteries 19.

FIG. 4 shows in greater detail the layout of the force sensor 1 a, ofthe push and pull element 14 and of its fastener 16, as well as of thehandle 18.

From FIGS. 3 and 4 it can be deduced that when the user pulls or pushesthe handle 18, this results in a forward or backward spring deformationof the band corresponding 14, 15, which deformation is detected by therespective extension-measuring gauge 1 a, 6 a and converted into anelectrical signal in accordance with that explained above. Due to theflexibility of the bands 14, 15, when the user is not pushing or pullingthe handle, released either intentionally or accidentally, the bandsreturn to their stop position and, as a result, the motion of the unitis halted.

The embodiment illustrated in the figures can be applied, by way ofexample, to a self-propelled mobile X-ray unit, of approximately 400 kgin weight. In this case use can be made of two GSC electric motors 3, 8,each with a power of 500 W and a torque of 15 Nm, two ANALOGUE DEVICEpower amplifiers, each of 500 W, which incorporate the preamplifiers 11,12 of the left feedback circuit 5 and the preamplifiers (not shown) ofthe right feedback circuit 10. To provide the user with a sensation ofheaviness which permits him to push and pull the unit with greatersecurity, it has been calculated that he should apply a force, inrespect of each hand, of between 0 (=stopped) and 4 kg when pushing +FI,+FD, or pulling −FI, −FD, detectable by the force sensors 1, 6. Thepower amplifiers 2, 7, multiply these pushing or pulling forces byfactors KI, KD which can be set for example in 11 and feed thecorresponding power to the electric motors 3, 8 so that they can propelthe wheels 4, 9 with the necessary forces +KIFI, −KIFI, +KDFD, −KDFD.When the operator is moving the unit on a downward slope and is pushingwith maximum force of 4 kg, this implies the unit will be travelling atthe maximum attainable speed. When moving the unit over a flat floor oron an upward slope, the maximum speed is reduced in order to achieve agreater drive force. Depending on the force applied, the operator cantherefore regulate the travelling speed over each surface.

1. A system for controlled operation of a device propelled by electricmotors, said system having: at least a first and a second drive wheelmounted in an axially opposed manner, each of said first and seconddrive wheels for propelling the device forward and backward; at least afirst independent electric motor for propelling the first drive wheeland a second independent electric motor for propelling the second drivewheel; a first and a second push and pull element; at least a firstindependent control means for the first independent control means forthe first independent electric motor and a second independent controlmeans for the second independent electric motor, each control meanshaving: a plurality of sensor means; an independent power amplifier; thesensor means: detecting the mechanical force of pushing and pullingapplied to the push and pull elements by a user standing on a floor;transforming said mechanical force into signals indicating degree anddirection of the mechanical force; capable of being operated separatelyso as to power each drive wheel selectively; the independent poweramplifier: amplifying the electric signals produced by the sensor means;supplying electric power to the electric motor; the electrical signalsbeing amplified in accordance with an amplification factor as a functionof the device weight; each drive wheel being propelled in accordancewith a torque corresponding to movement ordered by the sensor means;wherein: each power amplifier is provided with a feedback circuit thatmeasures a true value of an electric motor current said motor currentbeing proportional to a torque of the electric motor, the feedbackcircuit comprising: a comparator means for comparing said true valuewith a pre-established nominal value of an electric current needed toachieve movement of each drive wheel, a detecting means for detectingdifferences detected between the true value and the pre-establishedvalue, a transforming means for transforming said differences into errorsignals; an altering means for altering the electric input signals tothe power amplifier on the basis of said error signals, so as to makesaid power amplifier supply the necessary power to the electric motor sothat torque needed for producing movement ordered by the sensor means isgenerated by the electric motor.
 2. A system according to claim 1wherein each one of the control means further comprises a firstpreamplifier means for amplifying electric signals produced by thesensor means.
 3. A system according to claim 1 wherein the feedbackcircuit further comprises a second preamplifier means for amplifyingerror signals.
 4. A system according to claim 1 further comprising aconnecting element for coupling the push and pull elements, so as toallow a user to act selectively on the first or the second push and pullelement by pushing or pulling said connecting element.
 5. A systemaccording to claim 4, wherein the push and pull elements, the forcesensors, and the connecting element, are arranged so as to form handle.6. A system according to claim 4 wherein: the push and pull elementscomprise bands having a first extremity and a second extremity, thefirst extremity being coupled to the connecting element and the secondextremity being held immobile in fasteners; the force sensors compriseextension-measuring gauges arranged on the bands for detecting adeformation on each band when the connecting element is pushed orpulled.
 7. A system according to claim 1 wherein the at least two drivewheels comprises two drive wheels.
 8. A system according to claim 1wherein the device propelled is a mobile X-ray unit.